Loam
Four terrain types, unevenly split
We split the catalog two ways: canopy at or above 60% counts as shaded, below that counts as open. Grade at or above 5 degrees counts as steep, below that counts as mellow. That gives four combinations.
Half the catalog is shaded, gentle ground: heavy tree cover over a grade too slight to move much water on its own. Open, steep terrain is the rarest combination by a wide margin, at 8.3%. Most trail networks either hide their tread from the sun or give water somewhere to run, rarely both.
What each quadrant looks like on the ground
Shaded and steep
Hartland Mountain Bike Park and Little Mountain (both British Columbia) run full canopy over a 6.4° grade. Mont-Sainte-Anne (Quebec) pairs full canopy with a 7.3° grade. Bent Creek (North Carolina) reads 98% canopy at 8.8°. Shade slows drying, grade speeds it up, and the two work against each other.
Shaded and mellow
Bear Mountain Bike Park (British Columbia) sits at 100% canopy on a 0.9° grade. Crothers Woods (Ontario) reads 100% canopy at 3.4°. With little grade to help, these networks depend on time and sun angle more than most.
Open and steep
South Mountain Park & Preserve (Arizona) measures 0% canopy on an 11.8° grade, the steepest network with zero measured canopy anywhere in the catalog. Ridge to Rivers (Idaho) and Usery Mountain Regional Park (Arizona) both read 0% canopy with grades above 7°. Full sun and real pitch together, the combination that clears water fastest.
Open and mellow
Novi Tree Farm (Michigan) reads 56% canopy on a 0.3° grade. Grapefruit Trail (Florida) reads 51% canopy at 0.5°, and sits just 7 meters above sea level. Neither shade nor grade does much work here, which is why low, flat, open ground is often the last to firm up after rain.
Why aspect only sometimes changes the estimate
Loam's drainage model applies an aspect adjustment, sun-facing ground dries a little faster, shaded-facing ground a little slower, but only on grades of 5 degrees or steeper. Below that threshold, aspect makes no difference to the estimate at all.
The reasoning
On close to flat ground, which direction a trail faces barely changes how much sun hits it over a day. The effect only shows up once there is enough pitch for one side of the trail to angle toward the sun and the other away from it. Below 5 degrees, Loam treats aspect as neutral rather than guessing at an effect too small to measure reliably.
That means aspect matters for the 26.2% of the catalog sitting in the two steep quadrants, and is set aside for the 73.7% sitting in the two mellow ones. A north-facing network on a 1-degree grade and a south-facing network on the same grade get the same aspect treatment from the model. A north-facing network on a 12-degree grade does not.
The science behind the estimate
Loam starts with a simple physical fact: a trail does not dry just because the rain stops. Water has to enter the ground, move through or across the soil, and leave the trail environment. How quickly that happens depends on the soil, terrain, vegetation, recent weather, and how wet the ground already was.
Soil controls infiltration
Soils do not accept water at the same rate. USDA hydrologic soil groups range from high-infiltration soils such as deep sands and gravels to very slow-infiltration soils associated with clay, high water tables, or restrictive layers. Typical infiltration-rate ranges used in the hydrologic-group framework run from more than 0.30 in/hr for Group A to less than 0.05 in/hr for Group D when thoroughly wet.
Previous rain still matters
A storm does not start with an empty soil profile. USGS notes that soil already saturated from previous rainfall cannot absorb much more, so a larger share of the next storm becomes runoff. Recent weather therefore matters even when the latest storm was not especially large.
Terrain changes the water path
Slope changes how quickly water can move away from a surface. Low spots, drainage features, and trail geometry can change where water collects or leaves the tread. Soil classification and slope are separate pieces of the landscape, which is why both matter to a trail-condition model.
Drying is a water budget
After rainfall, water can remain in the soil, move downward or sideways, run off, or return to the atmosphere through evaporation and plant transpiration. Soil-water-balance models use these processes to estimate changing soil moisture and net infiltration over time.
Why Loam is not a rain timer
There is no useful rule that says every trail becomes rideable after the same number of dry hours. Starting moisture, infiltration behavior, terrain, canopy, and weather after the storm all change the answer.
That is the problem Loam is designed to estimate. The model combines public soil and terrain information with recent weather and network characteristics to estimate how conditions are changing. It is a model of likely trail conditions, not a sensor embedded in the dirt, and it never overrides an official closure.
What the research says
USDA and USGS hydrology work treats infiltration, soil moisture, runoff, canopy, land cover, slope, and evapotranspiration as interacting parts of the water cycle. Recent trail research adds an important piece: rainfall intensity and accumulated rainfall can strongly affect runoff and sediment generation on recreational trails, while wet conditions make trail surfaces more vulnerable to degradation.
USDA NRCS: Hydrologic Soil Groups
Soils are classified by infiltration and runoff behavior when thoroughly wet. The framework distinguishes four main groups and dual drained/undrained classes.
NRCS National Engineering Handbook →USGS: Infiltration and the Water Cycle
Explains how soil characteristics, saturation, land cover, slope, and evapotranspiration affect where precipitation goes.
USGS Water Science School →USGS: Soil-Water-Balance
A published water-budget model that estimates soil moisture, net infiltration, evapotranspiration, and canopy interception from gridded environmental data.
USGS SWB Version 2.0 →NRCS: RUSLE2
A USDA model for estimating soil loss caused by rainfall and associated overland flow, connecting rainfall and runoff to erosion risk.
USDA NRCS RUSLE2 →Fang & Ng, Journal of Environmental Management, 2026
A year-long field study found cumulative rainfall and maximum daily rainfall predicted runoff and sediment yield on recreational trails, with maximum daily rainfall the stronger predictor in that study.
Read the research →These sources describe the physical processes and research Loam draws from. They do not describe Loam's proprietary model or disclose its weights and thresholds.